The role of intracellular myoglobin in the support of intact functioning muscle in vivo will be studied. For these studies the in situ isolated dog gastrocnemius-plantaris muscle will be used. The muscle will be stimulated to contract isometrically and steady state measurements of oxygen consumption and tension generation will be made before and after administration of agents known to cause formation of non-functional myoglobin. These experiments will be performed under conditions of normoxia and hypoxia.